Android开发教程之ContentProvider数据存储

一、contentprovider保存数据介绍

一个程序可以通过实现一个contentprovider的抽象接口将自己的数据完全暴露出去，而且contentprovider是以类似数据库中表的方式将数据暴露的。那么外界获取其提供的数据，也就应该与从数据库中获取数据的操作基本一样，只不过是采用url来表示外界需要访问的“数据库”。

contentprovider提供了一种多应用间数据共享的方式。

contentprovider是个实现了一组用于提供其他应用程序存取数据的标准方法的类。应用程序可以在contentprovider中执行如下操作：查询数据、修改数据、添加数据、删除数据。

标准的contentprovider：android提供了一些已经在系统中实现的标准contentprovider，比如联系人信息，图片库等等，可以用这些contentprovider来访问设备上存储的联系人信息、图片等等。

在contentprovider中使用的查询字符串有别于标准的sql查询，很多诸如select、add、delete、modify等操作都使用一种特殊的url进行，这种url由3部分组成，“content://”，代表数据的路径和一个可选的表示数据的id。

content://media/internal/images 这个url将返回设备上存储的所有图片

content://contacts/people/ 这个url将返回设备上的所有联系人信息

content://contacts/people/45 这个url返回单个结果（联系人信息中id为45的联系人记录）

 如果想要存储字节型数据，比如位图文件等，那保存该数据的数据列其实是一个表示实际保存保存文件的url字符串，客户端通过它来读取对应的文件数据，处理这种数据类型的contentprovider需要实现一个名为_data的字段，_data字段列出了该文件在android文件系统上的精确路径。这个字段不仅是供客户端使用，而且也可以供contentresolver使用。客户端可以调用contentresolver.openoutputstream()方法来处理该url指向的文件资源，如果是contentresolver本身的话，由于其持有的权限比客户端要高，所以它能直接访问该数据文件。

二、使用方法

大多数contentprovider使用android文件系统或者sqlite数据库来保持数据，但是也可以以任何方式来存储。本例用sqlite数据库来保持数据。

1.创建一个接口，定义了一个名为content_url，并且是public static final的uri类型的类变量，必须为其指定一个唯一的字符串值，最好的方案是类的全称，和数据列的名称。

public interface iproivdermetadata {
  public static final string authority = "com.zhangmiao.datastoragedemo";
  public static final string db_name = "book.db";
  public static final int version = 1;
  public interface booktablemetadata extends basecolumns {
    public static final string table_name = "book";
    public static final uri content_uri = uri.parse("content://"
            + authority + "/" + table_name);
    public static final string book_id = "_id";
    public static final string book_name = "name";
    public static final string book_publisher = "publisher";
    public static final string sort_order = "_id desc";
    public static final string content_list = "vnd.android.cursor.dir/vnd.bookprovider.book";
    public static final string content_item = "vnd.android.cursor.item/vnd.bookprovider.book";
  }
}

2.实现sqliteopenhelper

public class contentproviderdbhelper extends sqliteopenhelper implements iproivdermetadata {
  private static final string tag = "contentproviderdbhelper";
  public contentproviderdbhelper(context context) {
    super(context, db_name, null, version);
  }
  @override
  public void oncreate(sqlitedatabase db) {
    ...
  }
  @override
  public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {
    ...
  }
}

3.创建一个继承了contentprovider父类的类

public class contentproviderdbhelper extends sqliteopenhelper implements iproivdermetadata {
  public contentproviderdbhelper(context context) {
    super(context, db_name, null, version);
  }
  @override
  public void oncreate(sqlitedatabase db) {
    ...
  }
  @override
  public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {
    ...
  }
}

4.在androidmanifest.xml中使用标签来设置调用contentprovider。

<provider
   android:authorities="com.zhangmiao.datastoragedemo"
   android:name=".bookcontentprovider"/>

5.增加数据

mcontentresolver = getcontentresolver();
string[] booknames = new string[]{"chinese", "math", "english", "sports"};
string[] bookpublishers = new string[]{"xinhua", "gongxin", "dianzi", "youdian"};
for (int i = 0; i < booknames.length; i++) {
  contentvalues values = new contentvalues();
  values.put(iproivdermetadata.booktablemetadata.book_name, booknames[i]);
  values.put(iproivdermetadata.booktablemetadata.book_publisher, bookpublishers[i]);
  mcontentresolver.insert(iproivdermetadata.booktablemetadata.content_uri, values);
}

6.删除数据

string bookid = "1";
if (!"".equals(bookid)) {
   contentvalues values1 = new contentvalues();
   values1.put(iproivdermetadata.booktablemetadata.book_id,bookid);
   mcontentresolver.delete(uri.withappendedpath(
                  iproivdermetadata.booktablemetadata.content_uri,
                  bookid), 
　　　　　　　　　　      "_id = ?",
              new string[]{bookid}
   );
} else {
  mcontentresolver.delete(
       iproivdermetadata.booktablemetadata.content_uri,
       null,
       null
  );
}

7.查询数据

cursor cursor = mcontentresolver.query(iproivdermetadata.booktablemetadata.content_uri,
            null, null, null, null);
string text = "";
if (cursor != null) {
  while (cursor.movetonext()) {
    string bookidtext =
cursor.getstring(cursor.getcolumnindex(iproivdermetadata.booktablemetadata.book_id));
    string booknametext =
cursor.getstring(cursor.getcolumnindex(iproivdermetadata.booktablemetadata.book_name));
    string bookpublishertext =
cursor.getstring(cursor.getcolumnindex(iproivdermetadata.booktablemetadata.book_publisher));
    text += "id = " + bookidtext + ",name = " + booknametext + 
          ",publisher = " + bookpublishertext + "\n";
  }
  cursor.close();
  mtableinfo.settext(text);
}

8.更新数据

string bookid1 = "2";
string bookname = "art";
string bookpublisher = "tiedao";
contentvalues values2 = new contentvalues();
values2.put(iproivdermetadata.booktablemetadata.book_name,bookname);
values2.put(iproivdermetadata.booktablemetadata.book_publisher,bookpublisher);
if ("".equals(bookid1)) {
   mcontentresolver.update(iproivdermetadata.booktablemetadata.content_uri,
              values2, null, null);
} else {
   mcontentresolver.update(uri.withappendedpath(iproivdermetadata.booktablemetadata.content_uri, bookid1),
              values2, "_id = ? ", new string[]{bookid1}
   );
}

三、小案例

1.添加strings.xml文件

  <string name="content_provider">contentprovider</string>
  <string name="add_data">增加数据</string>
  <string name="delete_data">删除数据</string>
  <string name="update_data">更改数据</string>
  <string name="query_data">查询数据</string>

2.修改activity_main.xml文件

<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.coordinatorlayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  android:fitssystemwindows="true"
  tools:context="com.zhangmiao.datastoragedemo.mainactivity">
  <linearlayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">
    <textview
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:layout_gravity="center_horizontal"
      android:text="@string/content_provider" />
    <linearlayout
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:layout_marginbottom="@dimen/fab_margin"
      android:layout_margintop="@dimen/fab_margin"
      android:orientation="horizontal">
      <button
        android:id="@+id/provider_add"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/add_data" />
      <button
        android:id="@+id/provider_delete"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/delete_data" />
      <button
        android:id="@+id/provider_update"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/update_data" />
      <button
        android:id="@+id/provider_query"
        android:layout_width="0dp"
        android:layout_height="wrap_content"
        android:layout_weight="1"
        android:text="@string/query_data" />
    </linearlayout>
    <textview
      android:id="@+id/table_info"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:text="@string/app_name" />
  </linearlayout>
</android.support.design.widget.coordinatorlayout>

3.添加iprovidermetadata接口

package com.zhangmiao.datastoragedemo;
import android.net.uri;
import android.provider.basecolumns;
/**
 * created by zhangmiao on 2016/12/20.
 */
public interface iprovidermetadata {
  public static final string authority = "com.zhangmiao.datastoragedemo";
  public static final string db_name = "book.db";
  public static final int version = 1;
  public interface booktablemetadata extends basecolumns {
    public static final string table_name = "book";
    public static final uri content_uri = uri.parse("content://"
            + authority + "/" + table_name);
    public static final string book_id = "_id";
    public static final string book_name = "name";
    public static final string book_publisher = "publisher";
    public static final string sort_order = "_id desc";
    public static final string content_list = "vnd.android.cursor.dir/vnd.bookprovider.book";
    public static final string content_item = "vnd.android.cursor.item/vnd.bookprovider.book";
  }
}

4.添加contentproviderdbhelper类

package com.zhangmiao.datastoragedemo;
import android.content.context;
import android.database.sqlite.sqlitedatabase;
import android.database.sqlite.sqliteopenhelper;
import android.util.log;
/**
 * created by zhangmiao on 2016/12/20.
 */
public class contentproviderdbhelper extends sqliteopenhelper implements iprovidermetadata {
  private static final string tag = "contentproviderdbhelper";
  public contentproviderdbhelper(context context) {
    super(context, db_name, null, version);
  }
  @override
  public void oncreate(sqlitedatabase db) {
    string tablesql = "create table if not exists "
        + booktablemetadata.table_name + " ("
        + booktablemetadata.book_id + " integer primary key autoincrement,"
        + booktablemetadata.book_name + " varchar,"
        + booktablemetadata.book_publisher + " varchar)";
    db.execsql(tablesql);
  }
  @override
  public void onupgrade(sqlitedatabase db, int oldversion, int newversion) {
    log.w(tag, "upgrading database from version " + oldversion + "to"
        + newversion + ", which will destroy all old data");
    db.execsql("drop table if exists " + db_name);
    oncreate(db);
  }
}

5.添加bookcontentprovider类

package com.zhangmiao.datastoragedemo;
import android.content.contentprovider;
import android.content.contenturis;
import android.content.contentvalues;
import android.content.urimatcher;
import android.database.cursor;
import android.database.sqlite.sqlitedatabase;
import android.net.uri;
import android.support.annotation.nullable;
import android.util.log;
/**
 * created by zhangmiao on 2016/12/21.
 */
public class bookcontentprovider extends contentprovider {
  private static final string tag = "bookcontentprovider";
  private static urimatcher urimatcher = null;
  private static final int books = 1;
  private static final int book = 2;
  private contentproviderdbhelper dbhelper;
  private sqlitedatabase db;
  static {
    urimatcher = new urimatcher(urimatcher.no_match);
    urimatcher.adduri(iprovidermetadata.authority,
        iprovidermetadata.booktablemetadata.table_name, books);
    urimatcher.adduri(iprovidermetadata.authority,
        iprovidermetadata.booktablemetadata.table_name + "/#",
        book);
  }
  @override
  public boolean oncreate() {
    dbhelper = new contentproviderdbhelper(getcontext());
    return (dbhelper == null) ? false : true;
  }
  @nullable
  @override
  public string gettype(uri uri) {
    switch (urimatcher.match(uri)) {
      case books:
        return iprovidermetadata.booktablemetadata.content_list;
      case book:
        return iprovidermetadata.booktablemetadata.content_item;
      default:
        throw new illegalargumentexception("this is a unknow uri"
            + uri.tostring());
    }
  }
  @nullable
  @override
  public uri insert(uri uri, contentvalues values) {
    switch (urimatcher.match(uri)) {
      case books:
        db = dbhelper.getwritabledatabase();
        long rowid = db.insert(
            iprovidermetadata.booktablemetadata.table_name,
            iprovidermetadata.booktablemetadata.book_id,
            values);
        uri inserturi = uri.withappendedpath(uri, "/" + rowid);
        log.i(tag, "inserturi:" + inserturi.tostring());
        getcontext().getcontentresolver().notifychange(uri, null);
        return inserturi;
      case book:
      default:
        throw new illegalargumentexception("this is a unknow uri"
            + uri.tostring());
    }
  }
  @nullable
  @override
  public cursor query(uri uri, string[] projection, string selection, string[] selectionargs, string sortorder) {
    db = dbhelper.getreadabledatabase();
    switch (urimatcher.match(uri)) {
      case books:
        return db.query(iprovidermetadata.booktablemetadata.table_name,
            projection, selection, selectionargs, null, null,
            sortorder);
      case book:
        long id = contenturis.parseid(uri);
        string where = "_id=" + id;
        if (selection != null && !"".equals(selection)) {
          where = selection + " and " + where;
        }
        return db.query(iprovidermetadata.booktablemetadata.table_name,
            projection, where, selectionargs, null, null, sortorder);
      default:
        throw new illegalargumentexception("this is a unknow uri"
            + uri.tostring());
    }
  }
  @override
  public int delete(uri uri, string selection, string[] selectionargs) {
    db = dbhelper.getwritabledatabase();
    switch (urimatcher.match(uri)) {
      case books:
        return db.delete(iprovidermetadata.booktablemetadata.table_name,
            selection, selectionargs);
      case book:
        long id = contenturis.parseid(uri);
        string where = "_id=" + id;
        if (selection != null && !"".equals(selection)) {
          where = selection + " and " + where;
        }
        return db.delete(iprovidermetadata.booktablemetadata.table_name,
            selection, selectionargs);
      default:
        throw new illegalargumentexception("this is a unknow uri"
            + uri.tostring());
    }
  }
  @override
  public int update(uri uri, contentvalues values, string selection, string[] selectionargs) {
    db = dbhelper.getwritabledatabase();
    switch (urimatcher.match(uri)) {
      case books:
        return db.update(iprovidermetadata.booktablemetadata.table_name,
            values, null, null);
      case book:
        long id = contenturis.parseid(uri);
        string where = "_id=" + id;
        if (selection != null && !"".equals(selection)) {
          where = selection + " and " + where;
        }
        return db.update(iprovidermetadata.booktablemetadata.table_name,
            values, selection, selectionargs);
      default:
        throw new illegalargumentexception("this is a unknow uri"
            + uri.tostring());
    }
  }
}

6.修改androidmanifest.xml文件

<provider
      android:authorities="com.zhangmiao.datastoragedemo"
      android:name=".bookcontentprovider"/>

7.修改mainactivity

package com.zhangmiao.datastoragedemo;
import android.content.contentresolver;
import android.content.contentvalues;
import android.database.cursor;
import android.net.*;
import android.os.bundle;
import android.support.v7.app.appcompatactivity;
import android.util.log;
import android.view.view;
import android.widget.button;
import android.widget.textview;import java.util.arraylist;
import java.util.list;
public class mainactivity extends appcompatactivity implements view.onclicklistener {private contentresolver mcontentresolver;
  private bookcontentprovider mbookcontentprovider;private textview mtableinfo;
  @override
  protected void oncreate(bundle savedinstancestate) {
    log.v("mainactivity", "oncreate");
    super.oncreate(savedinstancestate);
    setcontentview(r.layout.activity_main);
    button cpadd = (button) findviewbyid(r.id.provider_add);
    button cpdelete = (button) findviewbyid(r.id.provider_delete);
    button cpupdate = (button) findviewbyid(r.id.provider_update);
    button cpquery = (button) findviewbyid(r.id.provider_query);
    mtableinfo = (textview) findviewbyid(r.id.table_info);
    cpadd.setonclicklistener(this);
    cpdelete.setonclicklistener(this);
    cpquery.setonclicklistener(this);
    cpupdate.setonclicklistener(this);
  }
  @override
  public void onclick(view v) {
    switch (v.getid()) {case r.id.provider_add:
        mcontentresolver = getcontentresolver();
        string[] booknames = new string[]{"chinese", "math", "english", "sports"};
        string[] bookpublishers = new string[]{"xinhua", "gongxin", "dianzi", "youdian"};
        for (int i = 0; i < booknames.length; i++) {
          contentvalues values = new contentvalues();
          values.put(iprovidermetadata.booktablemetadata.book_name, booknames[i]);
          values.put(iprovidermetadata.booktablemetadata.book_publisher, bookpublishers[i]);
          mcontentresolver.insert(iprovidermetadata.booktablemetadata.content_uri, values);
        }
        break;
      case r.id.provider_delete:
        string bookid = "1";
        if (!"".equals(bookid)) {
          contentvalues values1 = new contentvalues();
          values1.put(iprovidermetadata.booktablemetadata.book_id,
              bookid);
          mcontentresolver.delete(
              uri.withappendedpath(
                  iprovidermetadata.booktablemetadata.content_uri,
                  bookid
              ), "_id = ?",
              new string[]{bookid}
          );
        } else {
          mcontentresolver.delete(
              iprovidermetadata.booktablemetadata.content_uri,
              null,
              null
          );
        }
        break;
      case r.id.provider_query:
        cursor cursor = mcontentresolver.query(iprovidermetadata.booktablemetadata.content_uri, null, null, null, null);
        string text = "";
        if (cursor != null) {
          while (cursor.movetonext()) {
            string bookidtext =
                cursor.getstring(cursor.getcolumnindex(iprovidermetadata.booktablemetadata.book_id));
            string booknametext =
                cursor.getstring(cursor.getcolumnindex(iprovidermetadata.booktablemetadata.book_name));
            string bookpublishertext =
                cursor.getstring(cursor.getcolumnindex(iprovidermetadata.booktablemetadata.book_publisher));
            text += "id = " + bookidtext + ",name = " + booknametext + ",publisher = " + bookpublishertext + "\n";
          }
          cursor.close();
          mtableinfo.settext(text);
        }
        break;
      case r.id.provider_update:
        string bookid1 = "2";
        string bookname = "art";
        string bookpublisher = "tiedao";
        contentvalues values2 = new contentvalues();
        values2.put(iprovidermetadata.booktablemetadata.book_name,
            bookname);
        values2.put(iprovidermetadata.booktablemetadata.book_publisher,
            bookpublisher);
        if ("".equals(bookid1)) {
          mcontentresolver.update(
              iprovidermetadata.booktablemetadata.content_uri,
              values2, null, null);
        } else {
          mcontentresolver.update(
              uri.withappendedpath(
                  iprovidermetadata.booktablemetadata.content_uri, bookid1),
              values2, "_id = ? ", new string[]{bookid1});
        }
        break;default:
        log.v("mainactivity", "default");
        break;
    }
  }
}